i. Field of the Invention
This invention relates to a novel malaria associated antigen (hereafter referred to as "CRA"), and more specifically relates to CRA that can induce a specific immune response to malaria as well as its production method.
ii. Description of the Prior Art
Plasmodium, i.e. malarial parasite has a peculiar mode of life. The living body, after being naturally infected with Plasmodium, produces anti-Plasmodium antibody, thereby exhibiting neutralizing ability and inducing humoral immunity. However, the neutralizing ability depending on antibody production does not last as habitual immunity, allows infection any number of times, and does not work as defensive immunity. In other words, it induces humoral immunity but does not induce the defense mechanism which might be derived from cellular immunity. This point is an obstacle to the prevention and the therapy of Plasmodium-infected diease, i.e. malaria and any sufficient immunological therapies can not yet be performed on malaria as things stand now. In fact, there are infected areas of malaria in all parts of the world, and said disease is demanding immediate attention because of ever increasing communication with various foreign countries. Thus, development of effective preventives and remedies is desired. Under these circumstances, on the basis of the classical experience in vaccine and considering the life cycle of Plasmodium, development of attenuated live vaccines obtained from various protozoa in the matured state, has been attempted. However, as predicted from the fact that natural infection with Plasmodium induces a very weak immunity which is described above, this attempt has not achieved a satisfactory result, and presents problems in safety which is due to live vaccine.
On the other hand, Takahashi et al. (Experimental Parasitology 49, 233-247, 1980) investigated the properties of the membrane of normal erythrocytes and the membrane of Plasmodium-infected erythrocytes being bound to various kinds of lectin. As the result of the investigation, they have found that there is a marked difference between the properties of the membrane of normal erythrocytes and the membrane of Plasmodium-infected erythrocytes being bound to lectin which can combine with mannose.